Samarium redox catalysis

Samarium (Sm) is one of the most important rare earth elements that have flexible entry to dual oxidation states (+3 and +2) under standard laboratory conditions, which has made it extremely valuable in chemical synthesis. Sm(II) reagents are widely used as versatile and stoichiometric reductants in organic synthesis. However, the use of a huge amount of metal salts and organic solvents causes cost and environmental issues, making Sm(II) reagents not potentially applicable to large-scale or industrial reactions. Therefore, the development of samarium-catalyzed reactions involving Sm(III)/Sm(II) redox cycling is of great importance. In this review, we summarize the state-of-the-art research on samarium redox catalysis. The key step of the redox cycle is the Sm(III)-to-Sm(II) reduction, which has thus far been enabled by various methods that will be outlined in this review.